A method using a synthesis of a plurality of successively shot images, and a method for removing (or suppressing) blurring within a single image, are known as techniques of correcting a hand tremor (a tremor caused by movement of a subject is not included here) in a shot image. For example, a method for sharpening an edge of an object or a texture within an image is known as a technique of removing blurring within a single image.
In normal cases, a pixel value (such as brightness, intensity, or the like) changes abruptly at an edge of an object or a texture within an image. A profile illustrated in FIG. 1 represents a change in a pixel value (brightness in this case) of an edge. A horizontal axis of the profile represents a position of a pixel. Since the brightness level ramps up and down at an edge, an area including the edge is sometimes referred to as a ramp area in this specification.
In FIG. 1, in an area (area A) where the brightness level is lower than a central level, the brightness level of each pixel is decreased. In contrast, in an area (area B) where the brightness level is higher than the central level, the brightness level of each pixel is increased. Note that the brightness level is not corrected outside the ramp area. With such corrections, the width of the ramp area is narrowed so as to sharpen the edge. This method is recited, for example, by J.-G Leu, Edge sharpening through ramp width reduction, Image and Vision Computing 18 (2000) 501-514.
However, if this method is applied to an entire image, an unnatural image sometimes results. For example, if the above described corrections are performed for an image where pixel values of an edge are uneven due to an influence of noise or the like, the edge sometimes becomes unnatural or irregular as a result.
A thinning process is proposed as a solution to this problem. However, the thinning process requires a large amount of computation for image processing. Accordingly, it is difficult to provide a thinning function, for example, to a mobile terminal or the like equipped with a camera function that demands a low power consumption and low cost.
An video image signal processing device having a pattern recognition unit, an LPF unit, and a selector so as to overcome a disadvantage caused by edge enhancement is known as a related technique. The pattern recognition unit calculates an evaluation function that indicates the degree of steepness of an edge portion of an input video image signal. The LPF unit includes a plurality of LPFs having mutually different filter characteristics. The selector selects a corresponding LPF based on the evaluation function obtained by the pattern recognition unit. Specifically, an output signal of an LPF for attenuating a high-frequency component in a wider area is selected when the edge of the input image signal is steeper. The selector outputs an input image signal unchanged if the signal has almost no edge portion. The image signal from the selector is input to an edge enhancement circuit (for example, Japanese Laid-open Patent Publication No. 2007-281538).